ath9k: clean up code duplication around ath_tx_start

Merge initial processing for the CAB queue and regular tx.
Also move ath_tx_cabq() to beacon.c and make it static.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
4 files changed